The reason for leaks after the repair is the lower tube is not forced all the way up into the upper tube, locking the lower seal in place to fully expand the rubber fitting in the pan.
This job can be done without removing the upper tube, at least on a SD.
The lower tube must be forced down into the pan removing the "O" ring from its seat in the rubber fitting. Now pry the rubber fitting up the tube and out of the pan.
The top of the lower tube will be below the cup end on the
upper tube.(still in place)
With the rubber fitting out of the pan there is just enough wiggle room to pull the lower tube up and out past the end of the upper tube.
Now clean the tube, apply some grease slide on the new rubber fitting and a new "O" ring in the bottom grove. Keep the "O" ring and grove dry, no grease. This helps to keep the "O" ring in place. Grease the "O" ring seat in the rubber fitting.
Sneak the tube back down the pan hole. Seat the new fitting all the way down into the pan. I use a crows foot for this from the top with a long extension.
Now the tube must be forced up into the upper tube ALL THE WAY.
Same crows foot under two gear clamps on the tube. Tap up with a small weighted hammer. You can see up into the upper tube with a flash light to see if the tube is all the way up.

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1984 300SD turbo 126
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God made me an atheist and who am I to question His wisdom